Disclosed are methods of decreasing the viscosity of an aqueous suspension of a water insoluble or sparingly soluble dietary fiber (compared to the viscosity of the dietary fiber alone), involving mixing the dietary fiber with water and a soluble compound (e.g., polysaccharide having a molecular weight of about 500 Da to about 1,000 kDa and a 1% solution viscosity of up to 10 mPa·s; or protein having a molecular weight of about 10 to about 500 kDa and a 1% solution viscosity of up to 10 mPa·s).
Psyllium seed husk (Plantago ovata) is a dietary fiber that is widely recognized for its health benefits, including relieving constipation, lowering cholesterol, improving insulin sensitivity and reducing postprandial hyperglycemia, prevention of colon cancer, and weight management (Anderson, J., et al., American Journal of Clinical Nutrition, 70: 466-473 (1999); Belknap, D., et al., Heart & Lung: The Journal of Acute and Critical Care, 26(3): 229-237 (1997); Davidson, M. H., et al., American Journal of Clinical Nutrition, 67(3): 367-376 (1998); Marlett, J. A., and M. H. Fischer, The Journal of Nutrition, 132(9): 2638-2643 (2002); Marlett, J. A., et al., American Journal of Clinical Nutrition, 72: 784-789 (2000); Pittler, M. H., and E. Ernst, American Journal of Clinical Nutrition, 79: 529-536 (2004); Ziai, S. A., Psyllium, I N: S. S. Cho & P. Samuel (Eds.), Fiber ingredients: Food applications and health benefits, pp. 393-426, 2009, CRC Press, Boca Raton, Fla.). It consists of a highly branched acidic arabinoxylan with β-(1,3) and β-(1,4) linkages in the xylan backbone, substituted with L-arabinose, D-galactose, D-rhamnose, D-galacturonic acid, and 4-O-methyl-D-glucuronic acid (Guo, Q., et al., Carbohydrate Polymers, 73: 35-43 (2008); Kennedy, J. F., et al., Carbohydrate Research, 75: 265-274 (1979); Yu, L., et al., Advances in Food and Nutrition Research, 55: 193-220 (2008)). It is an extremely hydrophilic material which absorbs several times its weight in water, thus swelling to form a gel or a highly viscous suspension, depending on the concentration. The high viscosity of psyllium husk is a major hurdle in terms of consumer acceptance. Numerous attempts have been made in the past to decrease the viscosity of this material in order that a physiologically significant amount may be consumed in a single serving. Most studies of this nature have focused on modification of the psyllium polysaccharides using physical, chemical, or enzymatic methods in order to decrease viscosity (Cheng, Z., et al., Journal of Functional Foods, 1: 44-49 (2009); Niu, Y., et al., Food Chemistry, 132(2): 1025-1032 (2012); Van Craeyveld, V., et al., Journal of Agricultural and Food Chemistry, 56: 11306-11311 (2008); Yu, L., and J. Perret, Lebensmittel Wissenschaft and Technologie, 36: 203-208 (2003); Yu, L., et al., Food Chemistry, 82: 243-248 (2003)). Yu et. al. (Yu et al., 2008) have reviewed in detail the various health benefits of psyllium husk as well as approaches to suppress its viscosity.
While there is some evidence that the health benefits, most notably the hypocholesterolemic effect, of psyllium husk are not compromised by some of the physical, chemical, or enzymatic modifications, it is not clear if such modifications will affect the other physiological effects of psyllium. In addition, most studies showing hypocholesterolemic effect of modified psyllium are in vitro studies (Cheng et al., 2009; Niu et al., 2012) or animal studies (Allen, K. G. D., et al., Journal of Agricultural and Food Chemistry, 52(16): 4998-5003 (2004)), and human feeding trials are lacking. In terms of ease of processing, the high water absorbing capacity and high viscosity of psyllium husk powder make it very difficult to process in wet form, necessitating the use of very large amounts of water which is then removed by various drying techniques using significant amounts of energy. Solid state enzymatic treatment procedures overcome this difficulty by processing the material in a dry state, but the treatment can be expensive due to the cost of the enzyme itself.
We have developed novel methods of decreasing the viscosity of dietary fibers (e.g., psyllium husk suspensions) based on the inclusion of a soluble compound (e.g., polysaccharide or protein) in the mixture. This approach does not involve partial replacement of the psyllium husk by another polysaccharide or protein, but rather the inclusion of an additional polysaccharide or protein material in the mixture. Thus if the soluble polysaccharide used is non-digestible, this approach can deliver a greater amount of fiber in a single serving than psyllium alone, while also decreasing the viscosity and thus improving palatability.